Vesicular Trafficking of Semaphorin 3A is Activity-Dependent and Differs Between Axons and Dendrites

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Abstract

Secreted semaphorins act as guidance cues in the developing nervous system and may have additional functions in mature neurons. How semaphorins are transported and secreted by neurons is poorly understood. We find that endogenous semaphorin 3A (Sema3A) displays a punctate distribution in axons and dendrites of cultured cortical neurons. GFP–Sema3A shows a similar distribution and co-localizes with secretory vesicle cargo proteins. Live-cell imaging reveals highly dynamic trafficking of GFP–Sema3A vesicles with distinct properties in axons and dendrites regarding directionality, velocity, mobility and pausing time. In axons, most GFP–Sema3A vesicles move fast without interruption, almost exclusively in the anterograde direction, while in dendrites many GFP–Sema3A vesicles are stationary and move equally frequent in both directions. Disruption of microtubules, but not of actin filaments, significantly impairs GFP–Sema3A transport. Interestingly, depolarization induces a reversible arrest of axonal transport of GFP–Sema3A vesicles but has little effect on dendritic transport. Conversely, action potential blockade using tetrodotoxin (TTX) accelerates axonal transport, but not dendritic transport. These data indicate that axons and dendrites regulate trafficking of Sema3A and probably other secretory vesicles in distinct ways, with axons specializing in fast, uninterrupted, anterograde transport. Furthermore, neuronal activity regulates secretory vesicle trafficking in axons by a depolarization-evoked trafficking arrest.

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